Structures for absorbing and dispersing mechanical energy are incorporated into shoes, sporting goods, clothing, protective equipment, vehicles and the like to provide user comfort and safety. Such structures function to absorb and distribute kinetic energy and thereby prevent damage or discomfort resultant from impacts. Energy absorbing and dispersing structures are frequently employed in shoes as innersoles, midsoles, heel liners, metatarsal supports, and padding on tongues and uppers, to cushion and comfort a wearer. Such structures are also incorporated into football helmets, crash helmets, ballistic vests and the like to minimize damage from energetic impacts.
Energy absorbing and dispersing structures are frequently fabricated from polymeric foam materials, of either the open or closed cell type. In other instances, such structures are comprised of bodies of fibrous materials, and in yet other instances, mechanical structures employing springs, pistons and the like are used as energy dispersing devices.
The operating range of an energy absorbing and dispersing structure is a parameter which must be adjusted for particular applications. If the force applied to such a structure exceeds its operational range, the structure will bottom out, and in some instances the structure will actually undergo irreversible break down. Bottoming out occurs when a structure can absorb no more energy, and ceases to provide any protection. For example, soles of shoes often include energy absorbing structures fabricated from open cell foam materials, and such materials provide a high degree of cushioning under relatively light stress loads; however, when high levels of force are applied to these materials, as for example when the wearer jumps, runs or stumbles, the cellular structure of the material flattens, and the innersole bottoms out allowing a jarring shock to be transmitted to a wearer's foot. This bottoming out can be accommodated by providing a thicker body of foam material; however, such increases in thickness are generally unacceptable in footwear. Furthermore, using a thicker body of foam in the sole of a shoe will produce discomfort and fatigue under low stress conditions, as encountered when walking or standing. Another approach is to employ a foam material having a higher degree of resiliency. This can be accomplished by utilizing a relatively stiff open cell foam structure, or by going to a closed cell foam, or other such structure which includes sealed air pockets. In either instance, the stiffer sole will provide adequate cushioning for high shock levels, but is very rigid under low shock conditions, thereby producing discomfort.
What is needed is an energy absorbing structure which has a very large dynamic operating range. That is to say, a structure which is fairly yielding under relatively low impact conditions, but becomes more rigid under high shock conditions. Furthermore, in many applications such as footwear, clothing and protective equipment, it is also desirable that any such energy absorbing and dispersing structure be relatively lightweight and thin.
Also, it is often desirable that an energy absorbing structure operate to redistribute energy. For example, an innersole of a shoe may advantageously redirect pressure from the ball of the foot to the arch region, so as to provide enhanced arch support under high impact conditions. Such energy redirection cannot be accomplished by foams.
A number of energy absorbing structures have been implemented in the prior art. For example, U.S. Pat. No. 4,566,137 discloses a protective helmet having a series of relatively large, interconnected, pneumatic chambers therein. Each of the chambers includes an internal baffle member which operates to control flow of air between chambers so as to allow for equilibration of air pressure when the helmet structure is being fitted and inflated, but to restrict air flow under high impact conditions. While the structure disclosed therein can provide a high degree of shock protection to a wearer's head, the necessity for employing an internal baffle structure dictates that the pneumatic chambers be few, large and relatively thick. This precludes use of this particular structure in configurations employing many relatively small, thin chambers. Thus, the device of the 137 patent cannot be readily adapted for use in shoes and the like.
Shoe sole structures comprised of a series of discrete or interconnected air-filled chambers are known in the art. Some examples of such structures are shown in U.S. Pat. Nos. 4,999,931; 4,670,995; 5,545,463 and 5,175,946, among others; however, none of these structures can function in an adaptive manner so as to adjust their resiliency in response to the magnitude of an applied force.
In some instances shoe soles have been manufactured which include resilient plates of metal or carbon reinforced polymer. These resilient plates can absorb shock over a fairly large operating range; but they do not act in an adaptive manner. In addition, they are bulky and expensive. Also, such energy absorbing plates are not capable of redistributing pressure, and they cannot be readily employed to cushion shoe tongues, uppers or heel liners.
Thus, there is need for an energy absorbing and dispersing structure which has a large dynamic operating range. Specifically, there is a need for a structure which can adapt to applied forces so as to effectively absorb both large and small shocks without being too rigid at low impact and without bottoming out or breaking down at high impact. There is also a need for a structure which can redirect force from one region to another. Furthermore, any such device should be easy to manufacture, miniaturizable and relatively thin and lightweight, so as to permit it to be employed in footwear, athletic equipment, clothing and the like.
As will be explained in detail hereinbelow, the present invention provides an adaptive, energy absorbing structure which adjusts its resiliency in response to applied force. The structure of the present invention is manufactured from a few relatively simple sheets of resilient, preferably polymeric, material, and does not require the affixation of additional elements thereto. These and other advantages will be readily apparent from the drawings, discussion and description which follow.